Electronic fade-in control system for phonographic reproduction or the like



July 11, 1950 J. w. BUcHHoLzER Erm.

ELECTRONIC FADE-IN CONTROL SYSTEM F' PHONOGRAPHIC REPRODUCTION OR THELIKE Filed oet. 4, 194e ATTORNEYS Patented July ll, 195i() UNITED STATESPATENT OFFICEI ELECTRONIC FADE-IN CONTROL SYSTEM FOR PHONOGRAPHICREPRODUCTION OR THE LIKE of Ohio Application October 4, 1946, Serial No.701,130

Claims.

The present invention relates to a system for the electronicreproduction of sound generated by the usual phonograph disk and isdesigned to improve upon such systems so as to eliminate certainobjectionable features ordinarily present when sound thus generated istransmitted to and reproduced over standard amplifier circuits.

While the invention has a wide range of utility and may be used for manypurposes, the use to which the invention has been especially adapted isin the reproduction of records of organ or vocal music such as oftenplayed during funerals or other events where it is desirable toreproduce the records without the customary objectionable noises whichhave heretofore been necessarily present.

One of the objects of the invention is the elimination of the initialsurface noise which is heard in phonographic reproductions as the needletravels over the spiral or lead-in portion of the sound track at thestart of the reproduction. This is an important element of the system asthe reproductions, especially at funerals, are conducted while the roomis very still and every discordant sound is highly magnified to the earsof the auditors and unless the initial surface noise is entirelysuppressed, the effect upon the auditors is very objectionable. Thesurface noise produced by the needle before it reaches the actual soundportion of the track will vary in intensity according to the material ofthe record or the extent to which it has been worn, and it is, therelfore, one of the achievements of the present invention that howeverstrong these noises may be they are completely suppressed so that nosound is reproduced until the needle reaches the first note ofmodulation on the record.

The principle upon which the first object of the invention is based isthat the signals produced by the surface noises, although to the earthey may seem to be intense, are, in fact, relatively weak and in allpractical cases are weaker than any sounds reproduced by the musicalmodulations. The system, therefore, provides a means which blocks offthe passing of weak signals such as would be produced by surface sounds,but will clear at the first musical note.

Another object of the invention is to avoid a sudden transition fromcomplete silence to the reproduction of musical sounds. If the musicalnotes were instantly produced at their full intensity, the impressionwould be highly objectionable. It is, therefore, one of the purposes ofthe invention to provide means by which the musical notes, as soonasthey appear, are automatically faded in from zero to the predeterminedvolume which is controlled by the gain setting of the audio system.

The accomplishment of the above specified objects creates a furthercondition which the present invention intends to rectify'. It frequentlyhappens that a pause or hiatus will occur inthe flow of musical tones ina composition or vocal piece. At such a time occurring during thereproduction of the music, it is not desired that the musical notesagain fade in, but that they should resume immediately at the fullintensity determined by the setting of the audio system. The systemwhich has been created, therefore, includes what may be termed a timedelay which may be set at any suitable point so that operation of thefade-in is circumvented without interfering with passing theconventional audio signals through the amplifier. The duration of thetime delay is selected so as to take care of the longest hiatus whichmay normally occur in selected records or compositions.

During such pauses as may occur when it is desirable to have the timedelay function, the surface noises may appear, but the pauses areordinarily of slight duration so that the ear does not catch them.

At the end of the musical notes, the blocking off of the surface noiseswill again take place and the complete reproduction will, therefore, bea perfect simulation of an actual musical performance without theobjectionable noises which are usually present.

The invention is employed as an addition to any of the usual or wellknown audio amplifier circuits and is interposed between thephonographic reproducer and the amplifier circuit. Itv

is not necessary to illustrate the amplifier circuit which is employed,as any well known arrangement may be adapted to the combination.

The drawing accompanying this application shows a control circuit whichhas been perfected.

way departing from the basic principles of the invention. On thedrawings appear many gures which give values for resistances, condensersand ferred to herein as they give cellent results the like, and thesehave been nc and are reand will serve as a guide to one see ing toemploy the invention, but they are not to be taken asv to the signalgrid II of the tube I.

vvoltage is rectified. element 31| of the tube 30 delivers a negativecontrolling. On the drawings also appear certain designations by whichstandard electronic units are known in the art, and these are given forthe same purpose and with the same reservations.

Referring to the drawing and with particular i reference to the meansemployed for suppressing the mechanical sounds which are caused by thetracking of the needle before the rst note of modulation on the disk: v

What is known in this art as a 1612 tube, indicated at I, serves as aconventional input amplier tube to anyA standard audio ampliiier circuitthrough the lead 2. This tube is ,blocked 01T from passing a weaksignal, such as is generated by the scratching noise from the needle, byv a negative charge delivered to the control grid of the tube indicatedat 3. This negative charge enters the system from a C-power supply atil, thence through a 1 megohm resistor, through a switch 6 controlled bythe relay l. The negative charge is conducted by the line 8 through anadditional 1 megohm resistor 9 tothe grid 3.

` As the voltage supply passing to the grid 3 is l I3ab and I3b areshielded by a casing I4 from the receptacle I2 to the points where theyenter the system.

As shown in the drawing, the line I3a contains two 250M resistors I5 toground. Between these resistors I5 is connected a line IG which is, inturn, connected through a .05 coupling condenser The line I3b isconnected through a 100M resistor II and a condenser I'Ib to the grid I8of the rst triode section of a standard type 6SN7 tube indicated at 20.The plate opposed to the grid I8 is indi-- cated at I9. It will thus beseen that as soon as a signal appears at the #4 terminal of thereceptacle I2, it is simultaneously transmitted to the grids II and I8;The tube 2l)Y is cascaded, asv

shown in the drawing, to provide two stages of Y resistance-Coupledaudio. The gain into the second section of this tube 2U is controlledAby a variable 750M resistor indicated at 22;

As shown in the drawings, the resistor 22 is :connected to the grid 24`of the second triode section of the tube 2D. The plates I9 and 2,5 areconnected to the B+ power line 28 through through a condenser 2 into onecathode 29 of a type 61-16 tube 30 in which the audio frequency Thecorresponding plate voltage to the line 33 which, in turn, delivers itto a switch terminal 31 and by the switch, to

be described, to the three condensers 35 arranged in parallel andconnected to three terminals 36a,

361? and 35C of the variable time delay switch The 6J5 tube 45 is sobiased that when there is no voltage (signal) appearing at the grid 33,the plate element 46 draws 6 milliamperes. The relay 1 heretoforereferred to is connected in series with the plate 56, and when thisamount of current, or slightly less, flows through the relay coil, thecoil is sufficiently energized to close the switch 5. Closing the switchcloses the circuit of the C-power supply which, as explained above,causes the negative charge to appear at the grid 3, suppressing anyaudio signal which may be transmitted to the grid and thus eiectivelyshutting olf the transmission ci any signal from the tube I to thefurther elements of the'audio amplifier.

As long as the signal received at the grids II and I 3 is weak, as ischaracteristic of surface noise, it is insuicient to increase the biasat grid 39 of the tube i5 and, therefore, the switch 5 remains closedand the negative charge delivered by the line 8 and appearing at grid 3suppresses the audio signal (surface noise) ap'- pearing` at gridl II.When, however, the needle reaches the modulated portion of the groove onthe record, the signal isv suiiiciently strong so that, passedby thetube 2o and ampliiied and rectified as explained, it appears as anegative voltage at the grid 39 of the tube All). As soon as thisnegative voltage appearsV at grid 3S, the increased bias causes thecurrent from the plate 6 to drop, and as soon as this occurs, the energyin the relay I drops to a point where the switch 6 opens. Opening of theswitch breaks the circuit of the C-supply to the grid 3 andthe tube Ithen functions in the normal manner, passing the musical tones on to theremaining stages of the audio amplifier, by which these sounds are thenreproduced and become audible.

It will be seen that the system, so far as has been described, insuresthat no audible sounds will be transmitted until the surface noisegenerated by the record is overcome by the louder musical tones. Thus isaccomplished the first stated object ofy the invention, i. e., thesuppression of objectionable noises caused by the scratching of theneedle in thersound track prior to the rst musical. modulation thereon.Thisl also suppresses the surface noise aty the end of the record,aftery the time-delay switch has ceased to function.

For accomplishing the second object of the invention, i. e., the fade inof the musical notes so that an abrupt commencement of the musicaltones-is avoided, theinstrumentality designated at 50 and entitled Fadein Speed is provided.

Between the 1 megohm resistor 5' and the 1 megohm resistor 9, there isconnected to the line 3a line 52'Wh-ich is connected to one terminal 53of the fade-in-speed control elem-ent 5t. Two additional terminals 511and- 55 are provided and the three terminals are connected in parallelthrough condensers 53a, Ella and 55a to the line 51. These condensersare preferably .5 mf. paper condensers. The elem-ent 59 is provided witha rotary plate t. InV the position shown in the drawing, currentdiverted from the line 3 passes through the condenser 53% only, but asthe' plate 60 is turned in clockwise direction the condenser capacitymay be doubled"` or tripled. The line 5l is connected to the commonground.

As soon. as theC-vol-tage passes through the switch il, thecondensersarefcharged, but when the main supplyl for the negative chargeat grid 3 is broken by the opening ofthe switch 6, the

condensers discharge to ground throughthe resistance network indicatedon the drawin-g which? permits the residual negative charge to beremoved from the grid 3 gradually so that the gain in the tube Iisgradually increased, thus causing the intensity of the audio signal togradually increase from zero to the predetermined intensity.

The speed at which the sound increases is, of l course, dependent uponthe capacity of the condensers, the slower the discharge rate to theground, the slower is the fade in of the audio signal. The rotatable.plate fpermi-ts the operator `to govern the rate of fade in subject tothe rated capacity of the condensers by cutting in' one, two or more.

In order to prevent the recurrence of the fade in after the musicaltones have started, in the event there is a pause in the record, thedevice designated as Time Delay and indicated by the numeral 40 isemployed. This element of the system has already been referred to.

The element normally functions only after the switch 6 has been opened.The rotary plate 6B is shown with an enlarged portion in contact withthe terminal 31 which leads to the grid 39 and also in contact with allthree `terminals 36a, b and c, but one, two or all three of theseterminals may be cut out, depending upon the extent to which the plateis moved between the stops 6|. These condensers receive a negativecharge while the musical tones are being transmitted through the tube2U, but when this is interrupted the voltage is gradually released tothe system from the condensers, maintaining the rectified negativevoltage during the pauses in the musical tones of the record. Thisprevents the relay from actuating the switch 6 and thus preserves thecircuits as they were at the start of the musicai tones. The time delayprovision may be decreased or :augmented within the capacity of thecondensers 35 by turning the plate lilk to cut out one or more of thecondensers.

The time delay switch is also intended to have a further function. Aterminal B4 is provided at the time delay switch which is connected bythe line G3 directly to the negative input line between the resistor 5and switch 6. If the plate 60 is turned counterclockwise to thefullextent permitted by the upper stop 6|, it makes contact with theterminal 64 and the terminal 3l, thus supplying a constant negativevoltage to the grid 39. This causes the current from the plate 46 todrop off, which through the relay opens the switch 6 and the fade in iseliminated. rThis position of the time delay switch is used when it isdesired to cut out the fade in altogether and will permit the system topass conventional audio signals through the amplifier.

The connections which have not been described but are shown on thedrawing are conventional. A standard milliammeter 12 is arranged to beplugged in to the jack 'H for the .purpose of indieating the properattract value and release value of the relay.

Other details and modifications may be suggested to those skilled in theart.

It will be seen that a system has been provided by which the soundsgenerated by the playing of a record may be reproduced electronicallywithout the transmission of the usual surface noise that precedes themusical tones. This is due to the practical application of the fact thatthe intensity of suchsounds is really less than the intensity of any ofthe musical tones, and by maintaining a negative charge fat. the grid'fthe` 1612 tube untilsuch time as the surface noise l switch. When,however, the time delay switchY ceases to function after the terminationof' the modulated tones due to the discharge from the condensers 35, thenegative charge will again appear at grid 3 of the tube l andthe'surface noise will -be eliminated. The period involved is usually ofsuch short duration that the surface noise does not affect the ear as itwould at'the start of the record.

The system shown and described herein is not limited to the specificpurpose for which it has been described .as it may be employed in thereproduction' of broadcast transcriptions and for other duties inconnection 'with electronic sound reproduction.

While, at many points in the foregoing, emphasis has been placed on theuseA of the above described system in the reproduction of musicalrecords, it will be understood that the lsystem shown herein willoperate just as effectively in the caseA of a speaking record.Therefore, in the claims we have employed the term modulated to coverthose portions of the record which may be either musical tones or anyother tones which `are found in the record and w l1 are intended to bereproduced, thereby d inguishing fromthe surface noise which precedesthe production intended to be reproduced.

What is claimed is:

1. In a system for electronic reproduc'qn of a phonographic record, saidsystem of the type having a phonographic reproducer and an audioarnplifying system, means interposed between the phonographic reproducerand theaudio amplifying system, said means comprising a source ofnegative charge connected to a control grid of a tube in the amplifyingsystem, a make and break contact in series with said source, actuatingmeans for said contact, electronic means energized by modulated impulsesfrom said reproducer, and

controlling said actuating means, and a delayk device to maintain saidcontact in open condition during a hiatus in the modulated tones.

2..In a system for electronic reproduction of a phonographic record,said system of the type having a phonographic reproducer and an audioamplifying system, means interposed between the :phonographic reproducerand the audio amplifying system, said means compr' g a source ofnegative charge connected to; control grid of a tube in the amplifyingsystem, a make and break contact in said source, actuating means forsaid contact, electronic means energized by modulated impulses from saidreproducer, and controlling said actuating means, and means operativewhen said contact is broken to cause a gradual increase in intensity ofthe transmission by the 2 audio amplifying system.

phonographic reproducer and the audio ampliphonographic records ortheVlike, said system of v the type having a phonographic reproducer and anaudio amplifying system, a tube connected to the phonographic reproducerand constituting a unit of an audio amplifying system, said tube havinga control grid, a constant source Of negativevoltage connected to thegrid, a switch in series with said source, condenser means connected tothe grid and said source, actuating means'for said switch, electronicmeans energized by modulated impulses from said reproducer, andcontrolling said `actuating means, said condenser means operating torelease at a predetermined rate a negative charge Afrom said grid afterthe switch is opened.

5. In a system for electronic reproduction of phonographic records orthe like, said system of the type having a phonographic reproducer andanali-dio amplifying'system, a tube connected to the phonographicreproducer and constituting a unit of an audio lamplifying system, saidtube having a control grid, a constant source of negative voltageconnected to the grid, a switch in said source, condenser meansconnected in parallel to the grid and said source, actuating means forsaid switch, electronic means energized by modulated impulses from saidreproducer, and controlling said actuating means, said condenser meansoper.

ating to release at a predetermined rate a, nega-f tive charge from saidgrid after the switch is opened, and a second condensermeans connectedto said electronic means and arranged to delay dissipation .of chargetherefrom, whereby said actuating means is not operated during a hiatusin the modulated pulses. 6.. In asystem for electronic reproduction ophonographic records or .the like,.said system 4of the type having an.amplifier circuit, means nor! mally impressing a negative charge on thegrid l of a `tube in the amplier circuit of said system suflicient rtoneutralize all signals at said tube, a

`switch controlling impressment of said charge,

current-responsive actuating means for said switch, means comprising athermionic tube with plate current controlling said actuating means and.in suiicient yamount to hold the said switch in position to retain saidnegative charge .on the said grid, and electronic means connected to.the

input Aof said system and .to .the `grid of said ther.-

mionic tube, and responsive to modulations in the input of said systemabove -a predetermined volume level to bias the grid of said thermionictube `and thereby lower the plate current value thereof below said.suiicient amount.

7. In a system for electronic reproduction of` phonograph records or`the like, said system of the type having an .amplier circuit, meansnormally impressing a negative charge on the :grid of a tube in theamplifier circuit of said ksystenr sufficient to suppress all signals atsaid tube, a switch controlling impressment of said charge,current-responsive actuating means for said switch, a thermionic tubenormally passing a current to said actuating means in sucient amount tohold the switcnin grid-charge-retain ing position, electronic meansconnected to the input of said system and :to-tbe grid of saidthermionic tube, and responsive to modulations in the input,- oi saidsystemabove a predetermined volume level, to lower the valuek of thesaid ourrent below said sufioient amount, and means t0 retarddissipation of the said charge on the said grid on release oi theSwitch..

8. In a systemfor electronic reproduction of phonograph records orthelike, said system of the type having an amplifier circuit, meansnormally impressing 'a negative charge on the grid of a tubein theamplifier circuit of said system suicient to suppress yall signals .atsaid tube, a switch controlling impressment of said charge,current-responsive actuating means for said switch, a thermionic tubenormally passing a current to said actuating means in sufficient amountto hold the switch inA grid-charge-retaining position, electronic meansconnected to the input of said system and to the gridof said thermionictube, and responsive to modulations in the input of said system above a.predetermined volume level, tolower the Value of said current below saidsuicient amount, means to retard the dissipation of the said charge onthe said grid on release of the switch, and means associated with themodulation-responsive means to retard restoration of ,said current tosaid sufcient amount during brief interruptions to the modulations inthe system.

v9. In a system for electronic reproduction of phonograph records or-thelike, said system of the type having vany amplier circuit, meansnormally impressing a negative charge on the grid of a tube in theamplifier circuit of said system suicient to neutralize all signals atsaid tube, a switch controlling impressment of said charge,current-responsive actuating means for said switch, means comprising va,thermionic tube with plate current leading to said actuating means, andin sulcient amount to hold the said switch in position to retain saidnegative charge on the said grid, .electronic means connected to theinput of said system and-to the grid of said thermionic tube, andresponsive to modulations in the input oi said system above apredetermined volumelevel to bias the grid of said thermionic tube andthereby lower the plate currentthereof below said sufficient amount, andmeans to retard dissipation of the negative charge on the rst-mentionedgrid on release of theswitch.

10. In a system for electronic reproduction of phonograph records or thelike, said system oi the type having an amplifier circuit, meansnormally impressing a negative `charge on the grid of a tube in theamplifier circuit of said system suiicient to neutralize all signals atsaid tube, a switch controlling impressment of said charge,current-responsive actuating means for said switch, means comprising athermionic tube with plate .current Vleading to said actuating means,and in sufficient amount to hold the said switch `in position to retainsaid negative charge .on said grid, electronic means connected to theinput of said system and to the grid of said thermionic tube, andresponsive to modulations in the input of said system above apredetermined volume level lto bias the grid of said thermionic tube andthereby lower the plate current thereof below said suicient amountmeansto retard dissipation of the negative .charge on thev first-mentionedgrid on release of the switch, and means -associated with themodulation-responsive means to retard restoration of said current tosaid sufficient amount during brief interruptions to the modulations inthe system.

JULIUS W. BUCHHOLZER. ROBERT B. DRABENSTOTT.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,864,890 Cloud June 23, 1932Number 10 Number

